I'm inclined to agree with Filth. This has never been an option in any other MMO I have ever heard of and don't see SE opening that door. Can you imagine the amount of calls they would get every day by allowing something like this?
SE: "Hello, Square-Enix"
Customer : "Hello SE. Yeah, Ummm, I'm taking my son to school and I won't be able to play for about 20 minu-- Well, lets just say a half an hour now, so I'm going to need my subscription placed on hold. I'll call you back if something changes between now and then, otherwise, yeah, just start service back up in a half an hour. Thank you."
(SE rep in the back ground): "Another one? We need to call a board meeting ASAP!"